This invention relates to a process for producing 2-hydroxymethylene-3,3-dialkoxypropanenitrile alkali metal salt and a process for obtaining alcoholic slurry of said compound from its synthetic reaction mixture.
2-hydroxymethylene-3,3-dialkoxypropanenitrile alkali metal salt (hereinafter called "ALVM.sub.2 ") is useful as the synthetic intermediate for vitamin B.sub.1, and has been produced from 3,3-dialkoxypropanenitrile (hereinafter called "DAPN") according to the normal pressure methyl formate process (Japanese Provisional Patent Publication No. 9755/1985) or the high pressure carbon monoxide process (Japanese Provisional Patent Publication No. 84526/1979 and Japanese Patent Publication No. 21623/1986), of which the latter is said to be more advantageous.
The normal pressure process is a process, in which the reaction between DAPN and methyl formate is carried out in the presence of an alkali metal alcoholate, and the reaction is permitted to proceed by expelling the methanol formed by the reaction out of the system. The high pressure carbon monoxide process is a process in which DAPN, carbon monoxide and methanol are allowed to react in the presence of an alkali metal alcoholate. In either process, a large amount of methyl formate coexists in the reaction mixture after completion of the reaction.
In spreading the methyl formate from the ALVM.sub.2 obtained by the reaction, it is important to obtain a slurry with good flowability without deterioration of ALVM.sub.2 and methyl formate. Further, if methyl formate can be taken out of the system, the reaction can be made more economical by reutilization thereof.
Methyl formate can be expelled out of the system by filtration or drying.
However, according to the method by drying filtration, because methyl formate has a boiling point of 31.5.degree. C. and an ignition point of -19.degree. C., which are both low, and also exhibits excessive toxicity to human body, special care is required for separation, recovery operation of methyl formate attached on the crystals, typically filtration operation, such as making the system a closed system, etc. On the other hand, since the filtrate obtained contains dissolved ALVM.sub.2 and sodium methylate, etc. remained therein, it cannot be utilized as such, and it is not necessary to perform separation operation such as distillation, etc. Besides, during the separation operation of methyl formate, deterioration (decomposition) of the remaining ALVM.sub.2 or decomposition of methyl formate by the catalytic action of sodium methylate are caused to occur, whereby recovery of methyl formate will be lowered.
The method by drying is the method, in which the reaction mixture slurry is led as such into a dryer and dried all at once by evaporation of methyl formate, etc., which may be expected to be an industrially advantageous method and experiments were conducted by use of various dryers provided with functions of stirring blade, etc. As the result, troubles of scaling and solidification particularly at the heat transmission surface occurred, and also deterioration (decomposition) of ALVM.sub.2 and lowering in recovery of methyl formate occurred similarly as in the case of the method by filtration. Thus, it may be judged to be industrially practiced with difficulty.
On the other hand, the above known high pressure carbon monoxide process comprises allowing DAPN, carbon monoxide and an alkali metal alkoxide to react in a solvent, including ethers such as ethyl ether, dioxane, tetrahydrofuran, etc.; aromatic hydrocarbons such as benzene, toluene, etc.; and so on.
However, the yield of the desired ALVM.sub.2 in the above known high pressure carbon monoxide process is at most about 97%, which cannot be said to be sufficiently satisfactory.